A gas laser of this type if subject of, for example, W. Germany patent application P No. 31 23 049.0. Similar lasers are described in W. German patent application P No. 30 44 023.4-33 and in the European application No. 81 101440.6. In the typical gas discharges of electrically pumped CO.sub.2 lasers of this kind, there occur several, partly independent chemical and physical processes that may lead to chages in the operation of the laser. Such effects may be caused, for example, by the absorption of ions, atoms or molecules at interior surfaces, by outgassing from surfaces and electrodes, by surface reactions, exchange reactions involving ions, atoms, molecules, and UV-photons, in the electrical discharge or else by diffusion processes across walls. Inasmuch as very complex reactions of this kind take place during gas discharges in lasers of the type described above, for example, the achievement of a state of stable equilibrium is relatively difficult. Therefore, the reactions have heretofore been more or less uncontrolled.